Long-term evolution of an estuarine ecosystem (the Gironde estuary case study)

• Main Author: Chaalali, Aurélie
• Other Authors: Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Université Sciences et Technologies - Bordeaux I, Benoît Sautour, Philippe Boët, Grégory Beaugrand
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2013
• Subjects: Fish; Copepods; Ecological niche; Multivariate analyses; Abrupt shift; Climate; Long-term changes; Estuary; Niche écologique; Poissons; Copépodes; Estuaire; Évolutions à long-terme; Changement climatique; Marinisation; Changement abrupt; Analyses multivariées; [SDV.SA]Life Sciences [q-bio]/Agricultural sciences; North Atlantic
• Online Access: https://tel.archives-ouvertes.fr/tel-01416128; https://tel.archives-ouvertes.fr/tel-01416128/document; https://tel.archives-ouvertes.fr/tel-01416128/file/CHAALALI_AURELIE_2016.pdf

Estuaries are among the most productive ecosystems on Earth. They constitute important areas for materials exchanges and play therefore a crucial part in biogeochemical cycles. Because of their location at the interface between marine and continental realms, they are also a migratory path for different fish species and in some cases, a nursery or a refuge area. These systems are submitted to many pressures, some of them being related to anthropogenic activities (e.g fisheries, maritime traffic, dredging, rising pollutions, etc.). These changes are superimposed to the intrinsic variability of these naturally complex ecosystems (characterized by a spatio-temporal variability of different environmental factors; i.e., temperature, salinity, turbidity, etc.). However, since recent years, an intensification of these alterations, being partly linked to the climatic component of Global Change, is observed. These changes, already documented, and their incidence on biological communities, constitute a challenge for the future management of estuarine ecosystems. However, due to a lack of long-term continuous time series, for now few studies on the long-term evolutions of estuarine systems have been reported. In this work, I used a unique set of data (35 years) provided by an ecological monitoring of the Gironde estuary (the model of estuary used in the study). The main objective of this thesis is to characterize the evolution of the whole system (physico-chemistry and biology) over the last three decades and to identify the forcings involved. The originality of this work comes from a global analysis of the main estuarine descriptors and from the evaluation of the relative contribution of global forcings. A study based on multivariate analyses, through an end-to-end approach, reveals two abrupt shifts in the state of the ecosystem of the Gironde estuary. These two changes appear to be linked to hydroclimatic fluctuations at a regional scale (North Atlantic basin) and also at a local scale. Some hypotheses on the possible ...